A SYSTEM FOR WIRELESS AND ENCRYPTED TRANSMISSION OF INFORMATION

Abstract: System for wireless and encrypted transfer of information between at least two communication units, where at least one electronic data carrier is used, and where the data carrier includes a with a unique code programmed and not changeable memory and a programmable memory which is written with encrypted information.

Description: A system for wireless and encrypted transmission of information Background of the invention During identification of people and vehicles contact less electronic data carriers, so called transponders, are used more and more often. Also so called smart cards are used in this respect. A transponder is a unit that reflects an illuminating electromagnetic high frequency signal and superimposes information on to it, usually without adding new energy to the signal. A smart card is a plastic card with a contact on the surface, through which a microprocessor in the card can be communicated for access to a memory in the card. Smart cards usually make use of encryption in some form, while encrypted transponders are uncommon. Encryptable smart cards are, as far as is known so far, always equipped with a microprocessor for their encryption function. In case of transponders a solution for automatic debiting of road charges is known, where a smart card temporarily is connected to the transponder via a contact while the vehicle is driven. The software controlled microprocessor of the card then performs the encryption operation, while the function of the transponder only is to transfer the information between the antenna of the transponder and the contact of the smart card. The transponder has in this case a microprocessor for handling of the serial protocol communication with the card since the data transmission in the card contact and via radio frequency are different in their nature both concerning transfer speed and communication protocol. Microprocessor solutions in data carriers have a disadvantage in that it for instance is not possible to supply the data carrier from a small battery that lasts for tenths of years. Instead external powering is needed, e g via a contact as in the smart card. Data carrier transponders without microprocessors however exist in a plurality of versions where encryption is not needed, e g for identification of animals or for automation of material flow, but in those cases usually only in versions that only can be read, or where the transponder memory is reprogrammable also after that the transponder has left the manufacturing process. Use of microprocessor based smart cards or non encrypted transponders therefore often causes a limitation in security and/or comfort. The transponders are relatively simple to falsify since commonly available read/write equipment can be used to change/copy their data, to be compared with the widespread criminality around magnetic cards. Systems for smart cards are not designed so that the cards can be quickly read and written in all applications such as at door passages. Smart cards have to be communicated through physical contact since their connection demands a galvanic contact, and the serial communication and the encryption operation in itself also takes time, making the comfort in their use limited. A special disadvantage is also the unreliability in the contact means of the communication units, that through oxidation, pollution or wear prevents use in dirty and very frequent applications. Contactless smart cards are available, but these have due to the current consumption of the microprocessor a very limited range, only a few millimetres. Transponders with encryption functions have, as earlier has been indicated, been studied e g for taking up road charges, but in this case power supply from the vehicle may be possible allowing for using a microprocessor. For road tolls it is extra hampering in case the function is slow, since traffic queues can build up. Either there is a need for more communication points along the movement track of the transponder, or it will have to stay in the communication zone until the encryption operation is completed. Known transponders have as earlier been said either a read only memory, e g of PROM type, or a memory that can be both read and written, e g in the form of a shift register or a RAM. Transponders with only a read only memory are difficult to falsify but have the limitation that they can not bring other information than their serial number and therefore demands data base communication in every communication point for decision about measure at the identification. Transponders with read/write memory can be used by decentralized systems, but are, as has been described before, possible to manipulate regarding their information. Decentralized systems have advantage of less vulnerability and faster function since connection to a central data base in real time is not needed. In centralised systems it is required that the data carrier identity is verified in relation to a data base before decision of measure to take after the communication. Solutions are thus missing regarding how to combine comfort (range), security (encryption, viewing and copy protection), compactness/life (current consumption) and speed (execution time in central data systems and/or transponders) in systems for people- and vehicle identification. The object and the most important characterizations of the innovation The object of the innovation is to make an electronic data carrier that gives a very secure, but at the same time flexible and easy to use function, where complete systems with comparatively simple infrastructure can be built. The identification will be flexible since the data carrier is of the transponder type. This means that it does not have to be brought in close contact with a communication unit, and that it is sufficient that it is in the vicinity of the communication unit to obtain a good communication. Thanks to the long range that can be created with transponder technology, especially if microwave frequencies are used, the data carrier can have many different designs and still fulfil its function. It can for instance be designed as a plastic card in credit card format, as a watch, or as a small box to carry e g in a ring holder for a bunch of keys. It can for instance be carried in a holder in the chest pocket, around the wrist or in a band around the neck. In vehicles it can for instance be mounted on the inside of a window for communication through it, but also many other ways to apply the transponder are possible to imagine. In a preferred embodiment a to the transponder incoming signal is modulated and coded with transponder data without adding new energy to the signal. This way the dimensions of the transponder, weight and cost will be low as compared to other solutions for two way communication e g radio transmitters and systems based on infrared and ultrasonic technology. The range can still be comfortably long, up to about ten meters. Information storage in the data carrier takes place partly in a read only memory and partly in a read write memory that not necessarily has to be readable. The read only memory is only possible to write once, preferably during manufacture, and is then not possible to change regarding its contents. This part of the memory is used for a unique code, a so called mark, so that every data carrier will be unique and so that it can't be mixed up with others. At writing of encrypted data into the data carrier, the information is encrypted together with its own mark and possible with a random number. This way a unique encrypted code is obtained for each data carrier, also if the information that is stored in different cards should be the same. This makes undue viewing of the transponder and falsification of it considerably more difficult. Another advantage with this measure is furthermore that it is usually not necessary to distribute passage lists or blacklists to the identification points, but only the system key that has been used for writing to the data carrier. With the aid of the system key, the distributed communication units are automatically able to judge if the data carrier is valid or not without need for calling a central system, which because of long response times in the central system may lead to boring waiting times. Another advantage with non calling systems is their robustness against errors. If the central computer or the communication network in a centralized system would fail, the system stops or has to operate in a spare mode where it at the moment can not judge whether the data carrier is valid or not. Another advantage with a system according to the invention is that the infrastructure in large systems is simplified, e g for payment in public traffic, for access control in buildings and in geographically distributed systems, for debiting in relation to operations of "drive in" nature e g parking and at many other payment operations such as in ski lifts, during fuelling and more or less in any area where debiting systems are used today. The simplification of the infra structure takes place through considerably lower load on the central communication network, since the validity of the data carrier can immediately and off line be judged at the communication point instead of by connection to a central data base. Simpler communication networks can thereby be used. The data carrier comprises in a preferred embodiment a write memory that is not possible to read, and a fast encryption algorithm that according to the invention is realized in hardware without microprocessor. In a write only register in the data carrier a data carrier key is written in the form of an encrypted number. The data carrier key is derived by encrypting the unique mark of the data carrier with a system key in the communication unit. An advantage with the described solution with a data carrier key and a hardware algorithm is that the system can ensure that nobody can repeat the behaviour of a valid data carrier. During identification the communication unit sends a random number to the data carrier. The data carrier encrypts the random number with the data carrier key and in its hardware included encryption algorithm, and retransmits the encrypted random number and the mark to the communication unit. The communication unit can now with the mark, the system key and the random number calculate the data carrier key and make the same encryption as the data carrier to check that the same response is received. A specific advantage by not using a microprocessor is that the encryption process is faster, especially since no time is needed for serially feeding of data between the high frequency area and the circuits of the microprocessor. Since the serial circuits can work in synchronism with the high frequency circuits, the communication time is considerably reduced. In a preferred embodiment the antenna of the data carrier and all electronic circuits are built together in one single unit to avoid internal data and power connections that may lower the reliability and that may make the unit more bulky. In difference to data carriers with microprocessor encryption, a data carrier with a hardware algorithm can be made much more lean on current, which gives smaller dimensions and lower cost at the same time that both speed and communication range are good. Many of the problems that are associated with microprocessor based wireless data carriers are thereby avoided. The data carrier can for instance be built into a thin card that is communicated at a large distance, for instance for car parking or automatic door opening, without need for bringing the data carrier in close contact with its communication unit. To show that an identification unit, e g a magnetic card or an identification transponder, is used by its owner, the security sometimes demands that a PIN-code (Personal Identification Number) is used during the identification. The PIN code can according the system described herein securely be stored in an encrypted form in the data carrier, and can compare with the code that is keyed in on a terminal at the communication point. The herein described solution with an encrypted PIN code in the data carrier thus makes it unnecessary to contact a central system to verify the PIN code, which as has earlier been described, gives a more robust and fast system without loss of security. A PIN code however limits the ease in the identification since it is necessary to key it in on a terminal. One can then imagine that the card is "opened" with a validity period by keying in the PIN code, e g at the first identification of the day. The validity period is written into the data carrier in an encrypted way and can last e g for the rest of the day. Description of embodiments The invention shall now be described more in detail with reference to the following drawing, where Figure 1 shows two communication units and a data carrier, Figure 2 shows communication with a data carrier with and encryption algorithm, Figure 3 shows a way to realize an encryption algorithm in hardware, Figure 4 shows communication with a data carrier where the data information has been encrypted, and, Figure 5 shows transferring a system key between two communication units. Figure 1 shows wireless and encrypted transfer of information between a first 1 and a second communication 2 by means of at least one data carrier 3. The data carrier thus brings encrypted information from one place to another, and is thereby a media. The data carrier can for instance be designed to be carried by a person and be communicated from the communication units by means of high frequency electromagnetic waves, e g microwaves 4, 5, so that the data carrier at writing is illuminated with a coded high frequent signal 5, alternatively during reading emits a reflex 4 where data, without new energy having been added to the high frequent signal, has been modulated onto a from a communication unit transmitted illumination signal 5, which in this case is continuous. The memory 6 of the data carrier contains partly a non programmable area 7 with a code that is unique to the data carrier, a so called mark, and partly a programmable but not necessarily readable part 8, a so called write memory, where variable data can be written in. In figure 2 is shown an example of an embodiment that admits that every data carrier from one instant to another answers with different codes, despite that its memory content is constant. This gives a falsification protection to the data carrier. The figure shows that the first 1 as well as the second 2 communication unit contains one and the same encryption key 10, and that at least a part 11 of the write memory 8 of the data carrier is readable from the outside. This memory part 11 is first written from the first communication unit with a data carrier key 12, created in the first communication unit from the before that from the data carrier read mark 7 and the earlier described system key 10. The data carrier key is this way written into a non readable part 11 of the write memory 8 of the data carrier. At a later instant the data carrier key 12 is used from the from outside not readable part of the data carrier's write memory 11 , together with a from the other communication unit received random number 13, as input parameters to a encryption device 14 in the data carrier. When the data carrier thus is written with the mentioned random number 13 from the second communication unit 2 the data carrier will emit a response 17 partly with its unique mark 7, partly with a code 16 that has been created by the earlier mentioned encryption device 14. The encryption device 14 creates a number 16 that is in such a relation to the received random number 13 and the earlier written data carrier key in 11, that the other communication unit 2, by encryption of the in the encryption device 14 encryptied answer from the data carrier and the openly given mark 7, with the system key 10, that consequently is in both communication units, and the random number 13 can judge whether the data carrier has been written by means of the first communication unit's system key 10, despite that the data carrier's response will vary from one communication instant to another since it is at each instant asked with different random numbers. Figure 3 shows an example of and embodiment with a hardware encryption algorithm that not is microprocessor based and software controlled, but that has been realised with simple logical circuits of shift register type. The encryption device in the data carrier can comprise shift registers with prime polynomial feedback. The algorithm is based on that the data carrier key 12 that the first communication unit has written into the data carrier is shifted around in the feedback shift register 30. The feedback comprises an EXOR gate 31. The data carrier key is thus changed, in a to the system known way, each time the algorithm is used. The data carrier key that is to be used at an encryption operation is derived by shifting bits from the feedback shift registers 30 through the EXOR gate 32 and into the shift register 33. The random number 13 that is obtained from the second communication unit is encrypted with the data carrier key in EXOR gates in 34 and is thereafter retransmitted together with the mark. In an embodiment of systems and devices according the invention, recognition of whether the data carrier has been written with a certain system key is thus obtained so that a data carrier in a certain group can be distinguished from data carriers in another group, alternatively from falsified units. Figure 4 shows an embodiment where at least a part 41 of the programmable memory 8 is readable from outside, and where the same data can be stored in different data carriers although the bit pattern in the memory part 41 through said encryption is different from one data carrier to another. The encryption according to figure 2 can, but does not need to, be part of the data carrier since certain applications don't need the earlier described function with an encryption algorithm in the data carrier. The first communication unit 1 first reads the unique mark 7 and then encrypts the mark with the basic information 46, and writes the encrypted information 42 in the write memory. When the same system key 10 is used in the other communication unit 2, the original information 46 of user data is recreated 45 since the from the electronic data carrier then read mark 7 and the system key 10 is used for decryption of the encrypted information 42 that has been stored in the programmable part of the data carrier memory 41. In addition to what has been described so far one can also, except mark 7 and system key 10 also use an in the first communication unit 1 created random number 43 when encrypting the information to the electronic data carrier's readable memory 41. In this case the recreated user data 45 are separated from the recreated random number 43 after decryption. Normally the random number is wasted after recreation. Encrypted information in a not readable part of the write memory 41 of the electronic data carrier, e g according to figure 4, can concern validity classed information intended to be carried only at certain communication instants, and represents for instance a validity time, a PIN code, a geographical area or a qualification class. Encrypted information in a readable part of the write memory of the data carrier, e g according to figure 4, can also concern value related information intended to be changed at each communication instant, such as monetary values or tics for fare tickets. The algorithm for writing and reading of data is normally symmetrical, and can for instance be of the DES type. The mark 7 in figures 1 , 2 and 4 can be permanented by that a for each data carrier individual and not changeable pattern is created in a silicon circuit in the logical circuits of the data carrier, e g by etching with laser or by with high current burn conductor paths in the circuits. It is of special advantage if this marking takes place already when the silicon circuit is manufactured, since very extensive equipment is needed in this case to reproduce a similar data carrier with a false mark. In figure 5 is shown how the earlier described system key 10 can be transferred from one communication unit to another. The system key 10 that in the first communication unit according to what has been described before is used to write encrypted information 12, alternatively 42, into the data carrier, and that for instance can be of a closed type such as the symmetrical DES algorithm, can be sent to the other communication unit by means of an encryption device 51 with an open key, e g according to the asymmetrical encryption algorithm RSA. The system key transfer from the first to the other communication unit is then made such that the open key 54 is created in the other communication unit by means of a for this second communication unit unique code and or a random number in 53, and is transferred to the first communication unit. The code can then e g include an identity that is stored in a not changeable memory in the communication unit. The first communication unit then encrypts its built in system key 10 with the open key 54 and retransmits the encrypted system key via a message 56 to the second communication key. The latter decrypts the system key message 56 with the aid of its unsymmetrical algorithm, the code 52 and its earlier possibly created random number so that the system key can be recreated and stored in the second communication unit. With this method only the other communication unit, that has access to its closed key 52 and the possible random number, can decode the message 56 with the symmetrical system key from the first communication unit, whereby open lines, e g telecommunication and data networks, can be used for the transfer 54, 56. With a transferred system key 10 the other communication unit can then communicate all data carriers that have been encrypted with the closed system key 10 in the earlier described way. A list of the identity of approved communication units is located in a communication unit register 55 in the first communication unit, to validate that the asking communication unit 2 belongs to a group of communication units that is approved for receiving keys from the first communication unit. To further increase the security in the validation back calling can be used, where the first communication unit after control of the identity of the second communication unit through interruption and recalling connects a new line to he other communication unit. This way the possibilities for a false calling unit to get access to information about the system is further reduced.

Claims: CLAIMS 1. System for wireless and encrypted transfer of information between a first and second communication unit by means of an electronic data carrier, and where communication between communication units and data carriers takes place by means of high frequent electromagnetic waves, such as microwaves, and where the data carrier during reading reflects a from the communication emitted illumination signal, characterized in that the memory of the data carrier includes an, after a first programming, not reprogrammable part with a for the data carrier unique code, a so called mark, and a programmable but not necessarily readable part, a so called write memory, where variable data is programmed according to an encryption algorithm in the communication unit. 2. System according to 1, characterized in that no microprocessor exists in the data carrier and that its function is realized by means of logical elements of the type of gates and flip flops that are not software controlled. 3. System according to any of the previous claims, characterized in that the data carrier is a separate and integrated unit that includes as well the antenna and all logical elements 4. System according to any of the previous claims, characterized in that as well the first and the second communication unit includes the same encryption key and that at least a part of the write memory of the data carrier is not readable from outside and that, in this part of the memory, the first communication unit writes in a data carrier key that is created by the first communication unit by encrypting with the system key,the mark, read from the data carrier, and that this data carrier key, at a later instant, is used by an encryption device in the data carrier to encrypt a from the other communication unit received random number and that the data carrier responds to the other communication unit with its mark and the encrypted random number, whereafter the other communication unit with the system key and the mark of the data carrier can encrypt the random number and compare the response from the data carrier and thereby show that the data carrier is programmed with a similar system key as in the other communication unit, despite that the response of the data carrier varies from one communication instant to another. 5. System according to any of the previous claims, characterized in that said encryption device in the data carrier has an encryption algorithm that is created according to one or several prime polynomials, and that it comprises logical circuits of the tape gates and flip flops and includes shift registers. 6. System according to any of the previous claims, characterized in that it selects out data carriers in a group that has been encrypted with a certain system key from data carriers in a group, that has been encrypted with another system key, alternatively from falsified data carriers. 7. System according to any of the previous claims, characterized in that at least a part of the programmable memory is readable from outside, and that the first communication unit, before it programs information in the write memory, first reads the unique mark of the data carrier and thereafter writes in the information and said mark encrypted with a system key in the communication unit, and that the same system key, together with the mark then read from the data carrier, is used in the other communication unit for decryption and control of the encrypted information that has been stored in the programmable memory of the data carrier. 8. System according to any of the previous claims, characterized in that in addition to mark and system key also a in the first communication unit created random number is used for encrypting information in the readable memory of the data carrier, and that user data after decryption in the other communication unit is separated from the random number. 9. System according to any of the previous claims, characterized in that encrypted information in a readable part of the write memory of the data carrier concerns validity classed information intended to be varied only at certain communication instants, e g comprising a validity time, a PIN code, a geographical area or a qualification class. 10. System according to any of the previous claims, characterized in that encrypted information in a readable part of the write memory of the data carrier concerns value related information intended to be varied at each communication instant, such as monetary values or clips for travel tickets. 11. System according to any of the previous claims, characterized in that the encryption algorithm for encrypted data in the data carrier is of DES type. 12. System according to any of the previous claims, characterized in that the mark has been permanented by creating a for each data carrier individual and not changeable pattern in a circuit of silicon in the logical circuits of the data carrier, including engraving with laser or burning with high current conductor paths in the circuit. 13. System according to any of the previous claims, characterized in that the system key that in the first communication unit is used to encrypt information that is written into the data carrier, such as a closed system key according to DES, is transmitted to the other communication unit by means of an open and asymmetrical encryption algorithm, e g according to RSA. 14. System according to any of the previous claims, characterized in that the transfer of the system key from the first to the other communication unit takes place by that the open key is created in the other communication unit by means of a for this second communication unit unique code and/or a random number. 15. System according to any of the previous claims, characterized in that the system operates at microwave frequency in the region 0,9 to 25 GHz. 16. Devices for wireless and encrypted transfer of information, characterized in that they comprise transponder units and/or communication units designed to operate in a system according to any of the claims 1 to 15.

Inventors: GUNNARSSON STAFFAN, WINQVIST GUNNAR, GUNNARSSON, STAFFAN, WINQVIST, GUNNAR
Applicants: GUNNARSSON STAFFAN, SAAB SCANIA COMBITECH AB, WINQVIST GUNNAR, GUNNARSSON, STAFFAN, SAAB-SCANIA COMBITECH AKTIEBOLAG, WINQVIST, GUNNAR
Application year: 1994
Main classification: H04K1
IPC codes: G01S13, G06K7, G06K17, G06K19, G07B15, G07C9, G09C1, H01Q1, H04B7, H04L9